Radio shielding conduit and method of making same



RADIO SHIELDING CONDUIT AND METHOD OF MAKING SAME Filed Sept. 29, 1952 ATTO RNE m m w W.

RADIOSHIELDING CONDUIT AND METHOD OF MAKING SAME Richard L. Elliott, Sidney, and Carl R. Joslyn, Bainbridge,

N.Y., assignors to The Bendix Corporation, a corporation of Delaware Filed Sept. 29, 1952, Ser. No. 312,046

1 Claim. (Cl. 154-8) This invention relates to flexible conduits or hose and more particularly to tubing adapted for use in protecting and radio shielding an electrical conductor or the like.

One of the objects of the present invention is to provide a novel radio shielding conduit which is extremely flexible and yet non-porous. Another object of the invention is to provide a novel flexible conduit wherein parts are novelly combined with non-metallic material to produce a moisture-proof structure.

Still another object is to provide a novelly constructed conduit which is adapted to satisfactorily withsand extreme high and low temperatures.

A further object is to provide a conduit of the above character which is not seriously affected by electrical corona or by exposure to oils, greases and gasoline.

Another object is to provide a novel method of fabricating conduits possessing the above advantages.

The above and further objects and novel features of the present invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention.

In the drawings, wherein like reference characters refer to like parts throughout the several views.

Fig. 1 is a side elevation view, with a central portion removed and parts broken away, showing one type of conduit made in accordance with and embodying the present invention; Fig. 2 is an enlarged detail view, partly in section and with parts broken away, illustrating the internal construction of said conduit, the section being taken substantially on line 2-2 of Fig. 1;

Fig. 3 is an enlarged sectional view taken on line 3-3 of Fig. l; and

atent Patented Dec. 20, 19 60 braided separately and inserted into one another or the larger diameter tubes may be braided directly on the smaller ones as a core. The smallest or inner tubeis generally braided on a solid removable core. I

The ends of the multiple layer conduit 1417 have the end portions of the layers thereof firmly secured together by means of solder and each said end is secured by means, such as solder, within the channel of an annular ferrule. The latter, as shown, is fabricated from two concentric cylinders 18 and 19 having overlapping internal and external flanges, respectively, which form a closed end that is preferably perforated. Said flanges are soldered together and the end portion of the conduit extends into and is soldered to the cylindrical and end walls of the ferrule. Preferably, the inner diameter of ferrule 18, 19 is substantially equal to the normal diameter of the innermost tube 17. If desired, ferrule 18, 19 may be made as a unitary piece.

The ferruled end of the tubing fits into a counterbore or recess in end fitting 12 and butts against an internal flange 20 therein. The inner diameter of flange 20 is preferably smaller than the inner diameter of ferrule 18,

.. the recess provided therein.

19 for a purpose to appear hereafter. The outer circumference of the ferrule and the inner closed end thereof are securely soldered to the wall of end fitting 12 in The outer end of ferrule 18, 19 is preferably flush with the end of the end fitting, but if desired, the outer cylinder 18 may be flared outwardly beyond the end of the fitting. The other end of the tubing is provided with a ferrule in a similar manner and is secured in end fitting 11 against a shoulder 21 therein.

For the purpose of rendering the conduit moistureproof and at the same time provide protection against the chafing of insulated wires passing therethrough, the above described conduit is treated in a novel manner to provide therein a lining 22 and at the same time provide thin layers 23, 24 and 25 of the lining material between adjacent layers of braided metal tubing. The layers 2325 are integrally connected to each other and to lining 22 through the porous braiding of the intervening braided metal tubes. The lining material should be non-porous, flexible and resilient. Additionally, the lining material should have good resistance to corona and for some uses should not contain volatiles. When set, said material should retain these properties when Fig. 4 is a further enlarged detail section taken on tremely adverse conditions, including vibration by wind currents and engine operation, exposure to extreme high and .low temperatures, electrical corona, grease, oil, gasoline, and moisture, wide variations in altitude, and rough handling by personnel. The novel. construction shown comprises a plurality of "superposed concentric tubes or sleeves 14, 15, 16. and 17, each of which is a braided wire tube. The strands when braided in a known manner to make up a tube may be constituted in various forms known to the art but in a preferred embodiment, each strand is made up of about eight small wires laid side by side to simulate a flat strip; -'Ihe tubes may be subjected to a wide range of temperatures and exposed to grease, gasoline and moisture. A suitable material should also be tough and have the ability to adhere to the braided metal tubing and withstand continual bending stresses. Elastomers, such as those having a polyvinylchloride base and silicone rubbers have been found suitable.

One lining material which has been found suitable for use in flexible conduits for radio shielding aircraft engine ignition systems, for example, is a synthetic plastic material known in the trade as a plastisol, i.e., a fluid dis persion of po-lyvinylchloride polymer in a plasticizer which may be converted by heat alone to an elastomeric vinyl compound. This material has a polyvinylchloride base with suitable plasticizers and a heat stabilizer. Suit able fillers may be used if necessary to vary the flow characteristics. A suitable com-position consists of ten parts by weight of polyvinylchloride, such as Geon #121, four parts of Rohm and Haas Paraplex G-SO (a polyester), two parts Paraplex G-60 (a polyester) and two parts of a heat stabilizer consisting of a mixture of Paraflex G50 and dibasic lead phthalate in equal parts. This material is prepared for application at normal room temperature. The Geon #l21'should be in the form of a fine powder, the plasticizers (Paraplex) are added in liquid form and the heat stabilizing mixture is added in finely powdered, well-mixed form. The ingradients are the mixed thoroughly, preferably under vacuum, and applied to the above described metal conduit structure in accordance with the novel method next des r b dt Apovel method iscomprehended'by this inventionfor fabricating the above described plastic .lined hose or conduit. When .the multiple layer braided metal conduit has been made and cut to desirable length, an end portion is circumferentially extended or expanded to the desired internal diameter by means of a mandrel. While the mandrel is in place, the layers of. said end portion surrounding it are soldered to one another. This may be accomplished by placing a ring of solder on the raw end of the conduit around the mandrel so that'it will flow between the layers of braided tubing to which a soldering flux has been applied. Preferably, the soldering should not be further from the end of the braided tubes than the depth of ferrule 18, 19.

The soldered end portion of the tubing is then coated with flux and inserted into a ferrule 18, 19 to the inner walls of which a-suitable flux has also'been applied. A liberalarnount of soldering flux is also placed on the exterior surface of .the ferrule and the latter is then sized by a compressive or swaging action to make it fit snugly into end fitting 11 or 12. After the sizing operation, the ferruled end of the tubing is inserted into the end fitting against a. ring of solder (not shown) placed on the shoulder 20 or 21. This end assembly is then heated, such as by electrical induction, to melt said solder ring and to remelt the solder in the end portion of the tubing to effect solder connections between the tubing and both parts 18 and 19 of the ferrule, between the end flanges of said parts and between the ferrule and the end fitting. Both end assemblies, including fittings 11 and 12, are effected in the same manner, and the completed conduit is thoroughly cleaned and dried preparatory to applying the lining and impregnating material. If the end wall of the "ferrule is perforated, some of the solder ring will flow into the ferrule and improve the joint.

To eflect impregnation and lining of the conduit with the plastisol described above or other similar compound, the inner surface of braided tube 17 is preferably wet with .a suitable primer to promote adhesion between the lining and the metal tubing. One suitable metal primer for this purpose when the tubes are made of nickel, is

commercially known as Unichrome #219PX and may be applied with a swab. Care should be taken not to apply the primer to surfaces to which attachment of the coating or lining is not desired. If maximum flexibility is .desired the primer should not be permitted to permeate the mesh of the braided tubes. After the treated conduit has been thoroughly dried and cooled, it is immersed in a... 1 a ner of el m xe a p e y r ted P tisghsompcuud tlabou room mp r t r h c mpound having the consistency or apparent viscosity which permit. only sluggish flow. A vacuum of about one inch of mercury absolute is then drawn on the container and its contents and maintained for a sufficient time, usually about 30 minutes, to remove all air and permit the com- "pound to permeate the entire structure of the conduit when pressure is subsequently applied. It may be desirable in some instances to immerse the conduit in the compound after the vacuum has been drawn. In this manner, it is easy to remove all air from the conduit structure. After releasing the vacuum, it is desirable to leave the conduit in the compound for about fifteen minutes or longer at atmospheric pressure to insure complete impregnation of'the multiple tube, i.e., complete filling of all voids by the compound.

The conduit is then removed from the compound and suspen d th the l ngi udina axis in a vertic p on to Permit e comp u drain fr y- D ain ng hould. sca nl einr r m. about n, m n tes t n h ur until th center ha s o s f c ent di mete t r ce v an insulated conductor or the like of desired size. It is then preferable to remove excess compound from the outer surface of the braid and from the end fittings before baking the conduit to cause the compound to set. In some cases it may be preferable however, to partially bake the coated structure before cleaning the surfaces which are not desired to "be coated. Baking for a total of about half an hour at 350 to 375 F. is adequate when the compound herein specifically described is used. After cooling, any excess compound remaining thereon is removed and the conduit is ready for use.

There is thus provided a sturdy, reliable and effective conduit made in accordance with a simplified method which effects a novel combination of plastic and metallic elements in such a manner as ,to insure long operating life of the conduit under severe adverse operating conditions. The conduit provided has moisture-proof, corona-resistant and heat-resistant qualities which are superior to those of similar conduits heretofore known and this superiority is attained while also improving the flexibility and toughness which in turn reduce breakage heretofore caused by vibration and bending. Additionally, the novel construction of the conduit is such as to obviate the deteriorating effects of metallic :friction, dirt, greases and gasoline and to afford better protection for electrical leads orthe like whichmay'be enclosed thereby.

Although only a single embodiment of the novel conduit comprehended by the invention is illustrated, by way of example, in the drawings, it is to be expressly understood that the invention is not limited thereto. For example, the end-fittings illustrated may vary widely in form, the number of layersof woven or braided tubing may be varied, and other known types of braided tubing may be employed. If desired, a layer or coating of the lining and impregnating materialmay be left on the outer surface of the conduit between the end-fittings. Various other changes may also be made, such as in the specific materials suggested, in the method of fabrication and in the design and arrangement of parts illustrated without departing from the spirit and scope of the invention, as will now be clear to those skilled in the art.

What is claimed is:

The method of making a flexible conduit which ineludes the steps of assembling a plurality of braided Wire tubes in telescoped relation to form a multi ply metallic hose, filling said hose and the spaces in and between the walls of said tubes with a sluggishly flowing liquid compound, suspending the hose with its longitudinal axis vertical until excess compound flows out of the hose leaving a central passage and a lining of said compound in the hose, and baking the impregnated hose to reduce said compound to a IlOIl-flOWEltbl solid.

References Cited in the file of this patent UNITED STATES PATENTS 1,726,957 Hughes Sept. 3, 1929 1,993,984 Wulle et a1 Mar. 12,1935 2,053,112 Schnabel Sept. 1, 1936 2,147,824 Webb Feb. 21, 1939 2,173,359 Freedlander Sept. 19, 1939 2,260,282 Grint Oct. 28,1941 2,338,266 Skoning Ian. 4, 1944 2,494,470 Carlson Jan. 10, 1950 2,577,049 Uline Dec. 4, 1951 2,611,930 Hill Sept. '30, 1952 2,647,296 Shive Aug. 4, 1953, 2,674,297 Greenwald Apr. 6,1954- FOREIGN PATENTS 576,551 Great, Britain Apr. 9, 1946 OTHER REFERENCES.

Product Engineering, Ap 1946., p es 304-306. S i n News Le ter, July .5, .1947, vol. 52, No. 1, page 4;, QPY D a 

